A roving frame generally comprises, between the cans which supply the sliver and the flyers which cooperate with the spindle to wind the roving on the core sleeves to form the roving bobbins, a drafting frame or unit which drafts the sliver.
The flyers can have a drive with a control speed and can have fingers which supply the roving to the core sleeve. After the repair of a roving break or following a doffing operation, it has been the practice to delay reestablishment of the so-called operating speed, i.e. the elevated speed at which the roving is applied to the core sleeve in the formation of the roving bottom, for a certain period of time with which the roving frame is driven at a substantially lower speed which can be referred to as a start-up speed, an inching or gentle speed, or simply as the slow speed.
The purpose of operating the roving frame at this substantially reduced speed is to allow the tension applied to the sliver to be minimized during the start-up phase and thereby possibly avoid a new break in the sliver in the region in which is meets the core sleeve and to prevent the sliver which is applied to the core sleeve initially from pulling off from the latter. Operation at a reduced speed also allows service personnel to monitor the start-up of the roving frame and the application of the roving or sliver to the core sleeves at such start-up. After this initial operation at a gentle speed, the roving frame can be accelerated to its normal operating speed.
It is known (see for example DE 31 19 00 C2) to avoid a sag in the sliver between the drafting frame and the flyer while the roving frame is operating at this gentle speed and thereby avoid a further possibility of sliver breakage. In this case during the start-up of the flyer after a doffing, the pressing fingers of the flyers can be automatically brought into contact with the core sleeves to cause the sliver ends to contact the capture regions of the empty sleeves. By avoiding the sliver sag, which can result because the drafting frame begins operation before the roving is wound up sufficiently or because the capture of the sliver end may be delayed, the operation during the gentle speed stage may be carried out with a slight increase in speed so that the winding of the sliver onto the core sleeve can occur at a speed which is slightly higher than the feed speed of the sliver.
When the pressing finger of the flyer is configured as described in DE 15 60 317, such that the pressing finger is urged against the capture region of the sleeve by the effect of centrifugal force, for the attainment of a sufficient pressing force, a certain minimum speed is required. This can, for example, be between 250 and 300 RPM.
On the other hand there is the danger that in the selection of such an elevated gentle speed after a fresh start-up of the roving frame following elimination of a sliver break, a force is applied at the point at which the sliver will meet the core sleeve that might result in a new breakage. Furthermore, if the gentle speed which is selected is excessive, it might cause injury to operating personnel who may be involved in manipulations in the region of a flyer.
As a consequence it has been proposed to provide a roving frame of the type described with two gentle speeds, i.e. two preliminary speeds prior to switch-over to the normal operating speed. A lower first gentle speed is used for the initial start-up of the machine following a roving break or for the start-up of a particular flyer position or the safe manipulation of the roving or sleeve in the machine. A second gentle speed, higher than the first but still significantly lower than the operating speed, is used for start-up of the machine following a doffing operation and where problems with sag are to be avoided. This system has an advantage that, following a doffing operation, one can operate selectively with the sufficiently high gentle speed that is required to ensure the application of the pressing finger to the sliver capture region of the core sleeve with sufficient force and thus reliable capture of the sliver end. However, when the first lower gentle speed is selected, especially after a break of the sliver or roving, the force applied to the sliver is significantly less so that a new roving break can be avoided.
It will be understood that the first or lower gentle speed can be used not only to avoid a new roving break in the region between the drafting frame and the bobbin after repair of a previous break, but also for the feeding of a sliver end from a can to the side of the respective drafting station of the drafting frame. The lower gentle speed, as a general matter, thereby ensures a lesser force in the region leading up to the bobbin over the entire machine path and can permit adjustment of the flyer to a certain angular position when, for example, a manual doffing process is to be undertaken.
To maximize productivity of a machine, the first or lower gentle speed should be high enough as to ensure that a roving break will not follow upon acceleration to the higher spinning forces or to endanger a service person whose hand may be in the path of moving parts of the spinning unit. The first gentle speed is preferably in the range of 90 RPM of the flyer.
This is, however, disadvantageous if a defined angular position of the flyers is to be set as, for example, can be necessary for manual doffing processes. When the latter is the available slow speed, many tries are frequently required for short-term actuation of the drive in order to bring about the desired position of the flyers. Furthermore, this latter gentle speed is too high for test runs designed to enable a service person to observe the spinning process or other specific functions of the machine.
Such functions cannot be ensured with the roving frame of DE 31 19 000 C2.